1. Field of the Invention
This invention relates to a method and a device for providing a wideband low noise information channel with ten kilovolt input-output electrical isolation.
2. Description of the Prior Art
The prior art in this field includes the well known optoelectronic isolators whereby a photoelectric cell receives a light signal from a light emitting diode. Optoelectronic isolators have significant disadvantages in that they tend to electrically drift, i.e., their performance varies with ambient humidity, temperature, and time. In addition, the optoelectronic isolation technology is inherently nonlinear and has a limited bandwidth, so that such devices typically can only carry signals with a maximum frequency of about 300 KHz.
Another device known in the prior art is a conventional electrical transformer with a V/F (voltage to frequency) converter. In this technology, a low frequency analog signal is input to a voltage-to-frequency converter which produces a series of voltage pulses in which the spacing between pulses varies with the voltage of the input signal. The resulting pulses are put through a conventional transformer for isolation purposes and converted back to an analog signal by a frequency-to-voltage converter. This device also has a limited bandwidth and cannot carry signals with a frequency as high as one MHz.
A third known device includes a pulse width modulator (PWM) which accepts the input signal and transforms it into a constant frequency (i.e., A.C.) signal but with a duty factor proportional to the input signal. This signal from the PWM is put through a conventional transformer or an optoelectronic isolator, and then through a discriminator (i.e., demodulator) to recover the input signal. This device cannot carry an input signal having a frequency equal to the modulating frequency; the maximum bandwidth is about one third or one fourth of the modulating frequency, which is a significant disadvantage for carrying high frequency signals since providing a three or four MHz modulating frequency is difficult.
Therefore there is a need for an information channel with high accuracy and high bandwidth (up to one MHz) that provides good electrical isolation (i.e., protection) between the input and output terminals.